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Blind Cave Fish May Shed Light on Human Body Clocks
(International Business Times Science News, September 7, 2011)

Blind cave fish have spent millions of years in the dark underground with no concept of day and night, yet scientists have found that they still maintain a working biological clock.

Researchers say that learning more about how these eyeless fish operate could yield new clues on how our own body clocks work.

The Somalian cave fish, Phreatichthys andruzzii, has an inner timekeeper that ticks on a roughly 47-hour cycle determined by food rather than sunlight. This is the intriguing find from an international team of scientists from Italy, Germany, and Spain that was published online September 6 in PLoS Biology.

The researchers hope that their finds will teach scientists more about the molecular pathways that govern such clocks, why they are important to organisms, and how creatures adapt when their clocks are no longer tied to cycles set by sunrise and sunset.

Most living things - animals, plants, some kinds of bacteria - follow the sun to set their daily clocks. Our internal clocks, known as circadian rhythms, govern our sleep patterns, feeding times, rise and fall of blood pressure, and other daily activities. While this clock generally operates on a 24-hour cycle, it is highly adjustable to the natural world, resetting on a daily basis by signals such as daylight to keep synchronized.

Nearly 50 species of fish worldwide have evolved to live without sunlight in caves. Many of these species have evolved into eyeless creatures.

"Cave fish give us a unique opportunity to understand how profoundly sunlight has influenced our evolution," researcher Cristiano Bertolucci, a chronobiologist at the University of Ferrara in Italy, told LiveScience.

Bertolucci and his colleagues compared the swimming behavior and clock-gene activity of the Somalian cave fish, which has lived up to 2.6 million years beneath the desert, with the relatively normal and closely related zebra fish.

Zebra fish run on a circadian clock, synchronizing with cycles of light and dark. As expected, the blind cave fish did not keep in sync with light and dark. However, when a different signal (feeding time) was used, both the zebra fish and cave fished matched, proving that cave fish clocks could work if given a relevant signal like food.

Researchers then gave the cave fish a chemical known to activate clock genes in normal fish. Surprisingly, the blind fish's circadian rhythms began moving on a bizarre 47-hour cycle.

While the cave fish can no longer operate on a 24-hour cycle, the test showed that the core components of the fish's biological clock remained functioning.

"We're watching a clock in the process of being broken," study author Nicholas S. Foulkes, of Karlsruhe Institute of Technology in Germany, told ScienceNews.

Foulkes added that in another million years or so, the cave fish may lose other important clock parts as well.

In another experiment, the team found that raising the temperature in the lab sped up the cave fish clock, while lowering the temperature slowed it down. This is also unusual, as most organisms' circadian clocks remain insulated from temperature change.

The findings confirm that the cave fish clock is still ticking, even though it can no longer be set by light. In contrast, zebra fish clocks respond to both light and food.

"This study sets the stage for a more complete understanding of how clocks respond to their environment," Foulkes said in the study.

For humans, there is great interest in the recent finding that light's effects on the circadian clock are mediated by non-visual pathways in the brain. Also, because the human circadian system is known to be important in health and illness (especially mental health), understanding our body clocks better can help address a core vulnerability in our own circadian system.

Researchers then gave the cave fish a chemical known to activate clock genes in normal fish.

Fossil Finds Complicate Search for Human Ancestor
(Erin Wayman, Smithsonian Magazine, September 9, 2011)

Australopithecines lived in Africa some 4 million to 2 million years ago. Scientists speculate that the australopithecines gave rise to our own genus, Homo, sometime around 2 million years ago, but there’s not much fossil evidence to show exactly when or how this happened. But last year, scientists led by Lee Berger of the University of Witwatersrand announced they had found a possible candidate ancestor of Homo: Australopithecus sediba. The species lived 1.977 million years ago and resembled Homo in many ways.

This week, the researchers published five papers in the journal Science that provide a more in-depth look at the species. Experts are excited about the fossils, but do not agree on where A. sediba belongs in the human family tree—and in some sense, its discovery muddies the picture of human evolution at this critical transition 2 million years ago.

The new studies analyze two partial skeletons found in Malapa Cave in South Africa: a 12- to 13-year-old male and an adult female. Here’s a rundown of the key findings:

Brain: The researchers studied the size and shape of the young male’s brain by taking X-ray scans of his skull and creating a virtual 3-D endocast. A. sediba had a small brain—420 cubic centimeters—only slightly bigger than a chimpanzee brain or half the size of a Homo erectus brain. But the shape and organization of part of the frontal lobe appear similar to Homo. The team says this may mean brain reorganization came before a big jump in brain size in humans.

Pelvis: The pelvis had a mix of australopithecine- and Homo-like traits. This is interesting because some of A. sediba’s more advanced traits, like the shape and orientation of the ilium, were thought to have evolved in the genus Homo to accommodate bigger-brained babies as they came through the birth canal. But since A. sediba had these features and a small brain, another factor probably drove the evolution of these traits; they could be the result of spending even more time walking on the ground and less time in the trees, the researchers suggest.

Hands and Feet: The team found a nearly complete wrist and hand for the species as well as a partial foot and ankle. The foot had a unique mix of traits not seen in any other hominid, suggesting A. sediba had its own form of upright walking and probably still climbed trees. The hand also indicates A. sediba was a climber, but it shows that the hominid had the musculature and anatomy necessary for a “precision grip,” when the thumb meets the fingertips. This movement is what allows you to thread a needle or hold a pencil—and it probably enabled A. sediba to make and use stone tools, the researchers say, although they have not yet found any tools with the species.

Here’s why A. sediba complicates things. For the species to be the ancestor of Homo, it had to have lived before the first species of that genus. That’s just common sense. And it’s true for what the researchers call the “earliest uncontested evidence” of Homo: Homo erectus, at 1.9 million years ago.

But then there’s the contested evidence. At roughly 2.4 million years ago—before A. sediba— a species called H. habilis (“handy man”) lived in Africa, although the researchers say there is disagreement over what fossils should be included in this species. If this handy man is really the earliest member of Homo, it’s hard to call A. sediba an ancestor (unless, perhaps, additional fossil finds push back A. sediba’s age).

In some ways, H. habilis is more human-like than earlier hominids; it had a much larger brain, for example. But in other ways, such as the anatomy of the hand, A. sediba is more human-like than H. habilis, Berger and his colleagues say. What does this all mean? It’s unclear. But at the very least, several different types of Homo-like hominids probably all lived at about the same time—making it a “most challenging endeavor,” the researchers say, to figure out how these forms relate to each other and which if any best represents the ancestor of our genus.

As paleoanthropologists like to say, more fossils may help clarify things—or muddle them even more.

evolution is an accurate picture of biological process.

Australopithecines lived in Africa some 4 million to 2 million years ago. Scientists speculate that the australopithecines gave rise to our own genus, Homo, sometime around 2 million years ago...